The invention relates to a pipe cutting and/or chamfering machine and to a process for cutting pipe sections from a pipe blank, in particular for cutting ring pieces from thick walled pipe blanks which ring pieces are adapted to be used in the manufacture of ball bearings.
Pipe cutting and/or chamfering machines of this type generally include a cutting head and clamping jaws which bear radially against the exterior surface of the pipe blank, a rotating face plate for uptake of at least one radially adjustable cutting tool and optionally at least one radially adjustable chamfering tool. This type of pipe cutting machine generally includes a clamping mechanism for grasping a cut pipe section and depositing it for further processing. This type of state of the art pipe cutting machine is described in the European patent No. 0 425 994 of the applicant herein.
In this known type of pipe cutting machine the pipe blank is deposited on a transport roller bed the parallel rollers of which are in alignment with the cutting head and at least one which is rotatably driven. By means of the driven roller(s) the pipe blank is transported through the cutting head and face plate against an adjustable stop member and then is clamped by means of clamping jaws. Thereafter the cutting operation is carried out. The stop member must be of rugged construction because it must not only properly position the pipe blank end, but must also absorb the inertial forces of the forward movement of the pipe blank, which is thick-walled and consequently has a large mass. After the pipe blank has been clamped by the clamping jaws the stop member is moved away from the pipe blank end in order to permit the clamping of the pipe section, which is to be cut off, to be grasped by the clamping mechanism and then to be deposited for further handling. Since this operational cycle repeats itself after each pipe blank feed advance, down times of the machine result which decrease the output of cut pipe sections. Furthermore, tolerance deviations of the width of the cut pipe sections may occur, in particular when, for example, metal chips or borings may lodge between the stop member and the end face of the pipe blank.
While the feed motion of the pipe blank by means of one or more driven rollers of a transport bed composed of a plurality of parallel rollers constitutes a relatively simple construction, it does, however, not permit the feed advance to be precisely adjusted to a given value. It is therefore necessary to move the pipe blank in each operational cycle with its end face against the adjustable stop member. Because there will inevitably occur in such an arrangement wear on the exposed cutting surfaces of the cutting tool, there results a gradual widening of the cut pipe section which can only be corrected if there is provided an adjustment mechanism for the stop member preferably along an additional CNC-axis.
In order to assure that the end face of the pipe blank abuts flush against the stop member, it is necessary to construct the roller bed so that, at the moment of contact by the stop member with the end face of pipe blank, there remains a sufficient driving force to cause a small additional rotation of the driven roller. This causes a high wear off the roller surface.
Finally an other drawback of the state of the art machines resides in the large waste of pipe section material that occurs in view of the fact that the transport rollers must be arranged in front of the input of the cutting head and a further advance of the pipe blank is no longer possible when no portion of the pipe blank is disposed on top of the driven roller. Furthermore, this pipe blank remnant can also not be further processed since a new pipe blank is used to move the pipe blank remnant through the cutting head. Since this pipe blank remnant is only still held by the clamping jaws in the cutting head, which have a small axial length relative to the axial length of the pipe blank remnant, these clamping jaws are therefore not suitable for holding and aligning the pipe blank remnant in an exact horizontal direction. The pipe blank remnant tilts and oblique pipe sections result from further cutting operations.
It is, of course, understood that ball bearings must be mass produced and preferably in a fully automatic operation with efficient as possible a use of the production machinery in order to minimize as much as possible the material losses due to cutting and/or machining in view of the raw material for ball bearings being expensive high alloy steel. Furthermore, the wear of the expensive machine cutting tools must be as low as possible. Low material losses can be realized by using band saws for machining the ball bearing rings which have a cutting width of 2 millimeter maximum. The cutting velocity of such a band saw is, however, not high and the useful service life of such band saws is low. This is due to the fact that a band saw can basically only cut transversely through a pipe and encounters throughout the cutting process hard zones in the region of the external and internal diameters of the pipe. To this must be added the fact that the cutting operation can not be carried out exactly normally to the pipe axis because the elastic unguided band saw can easily deviate from a preselected path in the region of the pipe, which makes a subsequent planing operation of the cut rings always indispensable.